Heads-up display

In the Call of Duty series, the HUD is not present at all times, and appears only when the player is low on ammo, sometimes when switching weapons or picking up a new weapon, and some other times. In Hardcore multiplayer modes, the HUD is limited to nothing but the kill-feed and a mini-map, which only appears when a UAV, Spy Plane, Blackbird, Advanced UAV, Orbital VSAT or H.A.T.R. is called in. They will also still see the names of teammates, the symbol showing they are carrying a bomb/flag, and the amount of flags captured.

Blood Splatter/Red Screen (Indicates health in every Call of Duty installment since Call of Duty 2)

Damage indicator, also known as "hitmarkers"

From Call of Duty: Modern Warfare 2 onwards, a Blast Shield/Flak Jacket indicator shows when an explosive hits an enemy using such equipment/perks. From Call of Duty: Modern Warfare 3 onwards, a Ballistic Vest indicator shows when damage hits an enemy wearing a Ballistic Vest. From Call of Duty: Ghosts, a red barrel icon indicates when an enemy is killed by a red barrel, or killed after being hit by a Thermobaric. A patch was also made that an orange hitmarker indicates a kill.